1. Field of the Invention
The present invention relates to a liquid-filled cylinder-shaped hydraulic vibration isolator, which can be suitably employed as a suspension bushing, an engine mount, a cab mount, and so on, of an automobile, for example.
2. Description of the Related Art
Conventionally, in a suspension mechanism of an automobile, a liquid-filled cylinder-shaped hydraulic vibration isolator has been known which is employed as a suspension bushing for connecting an automobile body with a suspension arm in a vibration-isolating manner. As illustrated in FIGS. 6 or 7, the conventional liquid-filled cylinder-shaped hydraulic vibration isolator comprises a main axial fitting 101, a stopper 102, an intermediate cylinder fitting 103, a rubber elastic body 104, an outer cylinder fitting 105, and a cylinder-shaped sealing rubber 106. The stopper 102 is fixed to an outer periphery of the central portion of the main axial fitting 101. The intermediate cylinder fitting 103 is disposed outside the main axial fitting 101 coaxially, and includes a pair of ring members 131, 131, which are disposed on the opposite ends thereof in the axial direction thereof and two bridging members 132, 132, which bridge between both of the ring members 131, 131 to form two window portions 133, 133, which are disposed in the peripheral direction thereof, together with both of the ring members 131, 131. The rubber elastic body 104 is interposed between the main axial fitting 101 and the intermediate fitting 103 to connect them integrally, and has two dented portions 144, 145, which are opened to the window portions 133, 133 of the intermediate cylinder fitting 103. The outer cylinder fitting 105 is disposed outside the intermediate cylinder fitting 103 coaxially, covers the openings of the dented portions 144, 145 by being subjected to drawing, and forms a main liquid chamber 151 and an auxiliary chamber 152, which are filled with a liquid xe2x80x9cLxe2x80x9d and which are communicated with each other by way of an orifice passage 153, between itself and the dented portions 144, 145. The sealing rubber 106 is fastened to an inner peripheral surface of the outer cylinder fitting 105 to seal the liquid xe2x80x9cLxe2x80x9d, which is filled in the main liquid chamber 151 and the auxiliary liquid chamber 152.
Note that, in this conventional liquid-filled cylinder-shaped hydraulic vibration isolator, while the main liquid chamber 151 and the auxiliary liquid chamber 152 are immersed in the liquid xe2x80x9cLxe2x80x9d to be filled therein, the outer cylinder fitting 105, which is disposed outside the intermediate cylinder fitting 103 coaxially, is reduced diametrically by subjecting it to drawing so that the openings of the respective dented portions 144, 145 of the rubber elastic body 104 are covered in a liquid-proof manner. Thus, the liquid xe2x80x9cLxe2x80x9d is filled in the main liquid chamber 151 and the auxiliary liquid chamber 152.
This conventional liquid-filled cylinder-shaped hydraulic vibration isolator is connected and fixed to an installation portion of either one of the automobile body and the suspension arm, which are to be connected, with the main axial fitting 101 by way of a bolt, etc., and is connected and fixed to an installation portion of the other one thereof by fitting the outer cylinder fitting 105 thereinto by means of pressing, and so on. Thus, the conventional liquid-filled cylinder-shaped hydraulic vibration isolator is disposed so that the main liquid chamber 151 and the auxiliary liquid chamber 152 are positioned along input directions of main vibrations, which are input into the conventional liquid-filled cylinder-shaped hydraulic vibration isolator. When the vibrations are input between the main axial fitting 101 and the outer cylinder fitting 105 in axially perpendicular directions with respect to the thus disposed conventional liquid-filled cylinder-shaped hydraulic vibration isolator, the vibrations can be attenuated effectively by the elastic action of the rubber elastic body 104 and the liquid-pillar resonance action of the liquid xe2x80x9cLxe2x80x9d which flows by way of the orifice passage 153 between the main liquid chamber 151 and the auxiliary liquid chamber 152.
By the way, when this conventional liquid-filled cylinder-shaped hydraulic vibration isolator is disposed in an automobile, a load of an automobile body is applied to it as an initial load in the axially perpendicular directions. Along with the application of the initial load, there occurs a tensile strain concentratedly in a part of the rubber elastic body 104. When the tensile strain thus occurs in the rubber elastic body 104, the rubber elastic body 104 starts deteriorating at the portion to lessen the strength so that the durability of the liquid-filled cylinder-shaped hydraulic vibrator degrades. Hence, the following operations are carried out generally in order to improve the durability. For instance, after forming the rubber elastic body 104 by vulcanization molding integrally between the main axial fitting 101 and the intermediate cylinder fitting 103, the rubber elastic body 104 is compressed preliminarily by subjecting an outer peripheral surface of the intermediate cylinder fitting 103 to drawing so as to relieve the tensile strain, which takes place accompanied by the application of the initial load.
In addition, in the conventional liquid-filled cylinder-shaped hydraulic vibration isolator, the sealing rubber 106, which is fastened to an inner peripheral surface of the outer cylinder fitting 105, is disposed in order to inhibit the liquid xe2x80x9cLxe2x80x9d, which is filled in the main liquid chamber 151 and the auxiliary chamber 152, from leaking. However, the sealing rubber 106 is formed independently of the rubber elastic body 104. Accordingly, since an additional and independent process is required for forming this sealing rubber 106 by vulcanization molding, it is one of the causes, which result in increasing the manufacturing cost.
On the other hand, it is possible to think of forming the sealing rubber 106 integrally with the rubber elastic body 104 so as to fasten it to an outer peripheral surface of the intermediate cylinder fitting 103. However, if such is the case, when the preliminary load is applied to the rubber elastic body 104 by subjecting the outer peripheral surface of the intermediate cylinder fitting 103 to drawing as set forth above, the sealing rubber 106 might be damaged by a drawing jig so that there might arise a fear in that it does not fulfil the sealing function, because the drawing is carried out to the intermediate cylinder fitting 103 by way of the sealing rubber 106.
The present invention has been developed in view of the aforementioned circumstances. It is therefore an object of the present invention to provide a liquid-filled cylinder-shaped hydraulic vibration isolator, whose manufacturing cost is reduced by disposing a sealing rubber onto an intermediate cylinder fitting and in which the intermediate cylinder fitting is subjected to even drawing without damaging the sealing rubber.
In an aspect of the present invention, a liquid-filled cylinder-shaped hydraulic vibration isolator, which can carry out the aforementioned object, comprises: a main axial fitting; an intermediate cylinder fitting disposed outside the main axial fitting coaxially and including a pair of ring members positioned on the opposite ends thereof in the axial direction thereof and a bridging member bridging between both of the ring members to form a plurality of window portions, disposed in the peripheral direction thereof, together with both of the ring members; a rubber elastic body interposed between the main axial fitting and the intermediate cylinder fitting to connect them integrally and having a plurality of dented portions, opened to the window portions of the intermediate cylinder fitting; an outer cylinder fitting disposed outside the intermediate cylinder fitting coaxially, covering the openings of the dented portions by being subjected to drawing and forming a plurality of liquid chambers, filled with a liquid and communicated with each other by way of an orifice passage, between itself and the dented portions of the rubber elastic body; a sealing rubber disposed between the intermediate cylinder fitting and the outer cylinder fitting to seal the liquid filled in the liquid chambers; the respective ring members of the intermediate cylinder fitting including a drawn major-diameter portion positioned on an outside in the axial direction thereof and being subjected to drawing and a minor-diameter portion disposed inside the drawn major-diameter portion by way of a stepped portion, formed as a smaller diameter than that of the drawn major-diameter portion and having a plurality of slits formed along the peripheral direction thereof; and the sealing rubber being fastened to outer peripheral surfaces of the minor-diameter portion and the bridging member so as to enclose the window portions of the intermediate cylinder fitting.
In the liquid-filled cylinder-shaped hydraulic vibration isolator according to the present invention, when a preliminary load is applied to the rubber elastic body by subjecting an outer peripheral surface of the intermediate cylinder fitting to drawing, the drawing is carried out while a drawing jig is directly brought into contact with the drawn major-diameter portion of the ring members, on which the sealing rubber is not positioned. Hence, the sealing rubber is not damaged by the drawing jig. Further, since the minor-diameter portion of the ring members is provided with a plurality of the slits along the peripheral direction, the minor-diameter portion and the bridging member are reduced diametrically substantially equally to follow the drawing of the drawn major-diameter portion. Therefore, the entire intermediate cylinder fitting is drawn substantially evenly by subjecting only the major-diameter portion to the drawing. Thus, it is possible to apply the most suitable preliminary load to the rubber elastic body, and accordingly it is possible to improve the durability.
Moreover, in the liquid-filled cylinder-shaped hydraulic vibration isolator according to the present invention, since the sealing rubber is fastened to the outer peripheral surfaces of the minor-diameter portion and the bridging portion, which are reduced diametrically substantially equally to follow the drawing of the drawn major-diameter portion, the crimping allowance (i.e., the portion of the sealing rubber which protrudes radially beyond the outer peripheral surface of the drawn major-diameter portion) of the sealing rubber does not vary before and after the drawing. Hence, it is possible to secure the designed crimping allowance for the sealing rubber with ease. Note that, since the sealing rubber is disposed on the intermediate cylinder fitting, which is connected integrally with the rubber elastic body, it is possible to simultaneously form the sealing rubber in the same manufacturing process as the process for forming the rubber elastic body by vulcanization molding. Thus, it is possible to reduce the manufacturing cost by reducing the man-hour requirement for vulcanization.
Therefore, in accordance with the present liquid-filled cylinder-shaped hydraulic vibration isolator, it is possible to reduce the manufacturing cost by disposing the sealing rubber on the intermediate cylinder fitting. Further, it is possible to subject the intermediate cylinder fitting to even drawing without damaging the sealing rubber.
In a further aspect of the present invention, the present liquid-filled cylinder-shaped hydraulic vibration isolator employs the slits, which are disposed at equal intervals in the peripheral direction of the minor-diameter portion.
With such an arrangement, when an outer peripheral surface of the drawn major-diameter portion of the intermediate cylinder fitting is subjected to drawing, it is possible to diametrically reduce the minor-diameter portion, which is reduced diametrically to follow the drawing of the drawn major-diameter portion, much more equally. Thus, it is possible to realize much more even drawing for the intermediate cylinder fitting.